Spread of Forest Pests and Pathogens in the Northern Hemisphere

There are four main forest regions in the northern hemisphere, each containing many of the same genera of trees. An organism (insect, fungus etc.) living in balanced relationship with its host tree in one of these forest regions may cause major damage if moved to another. Examples of pest and disease problems analysed include Chestnut blight, White pine blister rust, Gypsy moth, Balsam woolly aphid, Dutch elm disease, Pine wilt disease and Beech bark disease.